Browsing by Author "Bal, Burak"

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Functional Surfaces of the Future: Integrating Texturing and Coatings for Superior Performance
(Elsevier Sci Ltd, 2025) Yuan, Yanjie; Louhichi, Borhen; Heidarshenas, Behzad; Alrasheedi, Nashmi H.; Bal, Burak; Hussain, Ghulam
Current surface texturing and coating methods exhibit performance improvements but face significant limitations, including inconsistent durability, scalability restrictions, and inadequate integration of their properties. Integrating these approaches can effectively address these challenges. Modern methods, such as laser machining and additive manufacturing, are paving the way for mainstream applications, offering the opportunity to develop new high-performance surfaces in various fields. For instance, combining laser texturing and advanced coating can address durability issues by developing precise patterns and strong adhesion. The combination of surface texturing and coating improves tribological performance and enhances service maintenance by overcoming the limitations of conventional methods. This offers advanced capabilities for various applications, including medical implants and marine environments. In this context, the synergistic application of texturing and coating technologies is expected to be crucial in developing high-performing advanced materials suitable for various applications. This study reviews the progress on synchronizing texturing and coating approaches. Governing mechanisms and controlling factors are identified and discussed. The benefits of applying synergetic approaches to surface performance are recorded. Optimum conditions to realize the best results are determined. Current challenges, emerging trends, and potential solutions to address these issues are proposed.
Accurate Prediction of Residual Stresses in Machining of Inconel 718 Alloy through Crystal Plasticity Modelling
(2023) Bal, Burak; Cetın, Barıs; Yılmaz, Okan Deniz; Kesriklioglu, Sinan; Kapçı, Mehmet Fazıl; Buyukcapar, Ridvan
Artık gerilmelerin belirlenmesi ve değerlendirilmesi, savunma, havacılık ve otomotiv endüstrilerinde kullanılan bileşenlerin arızalanmasını önlemede çok önemlidir. Bu çalışmanın amacı, Inconel 718'in işlenmesi sırasında oluşan artık gerilmeleri doğru bir şekilde tahmin etmek için bir malzeme modeli sunmaktır. Ortogonal talaşlı imalat testleri, çeşitli kesme ve ilerleme hızlarında gerçekleştirilerek, Inconel 718'in işlenmesinden sonraki artık gerilmeler, X-Ray ışın kırınımı ile karakterize edildi. Bu süper alaşımın mikroyapısal girdilerini ticari olarak temin edilebilen bir sonlu eleman yazılımına (Deform 2D) aktarmak için bir viskoplastik kendi içinde tutarlı kristal plastisite modeli geliştirildi. Ayrıca simülasyonlar klasik Johnson - Cook malzeme modeli ile aynı işleme parametrelerinde yapıldı. Bu çalışmada elde edilen simülasyon ve deneysel sonuçlar, kristal plastisite tabanlı çok ölçekli ve çok ölçekli malzeme modelinin, mevcut modele kıyasla Inconel 718'in işleme kaynaklı kalıntı gerilmelerinin tahmin doğruluğunu önemli ölçüde geliştirdiğini ve yüzey kusurlarını en aza indirmek için kullanılabileceğini göstermiştir. Geliştirilen bu model, kesilmesi zor malzemelerin işlenmesinde yüzey kusurlarını ve üretim denemelerinin maliyetini en aza indirmek için kullanılabilir.
Zırh Çeliklerinin Hidrojen Gevrekliği Davranışlarının Deneysel Yöntemlerle Belirlenmesi ve Hidrojen Giderme Operasyonunun Optimizasyonu
(Abdullah Gül Üniversitesi, Fen Bilimleri Enstitüsü, 2021) Bayram, Ferdi Caner; Bal, Burak
Hidrojen kırılganlığı veya hidrojen destekli çatlama olarak da bilinen hidrojen gevrekliği, hidrojen atomlarının metallerin kristal kafes yapısına girmesi, difüzyonu ve maruz kalması nedeniyle bazı metalik malzemelerin (yüksek mukavemetli çelikler, titanyum alaşımları, alüminyum alaşımları, vb.) kırılgan hale geldiği veya kırıldığı karmaşık bir süreçtir. Boru hattı çelikleri, zırh çelikleri, gelişmiş yüksek mukavemetli çelikler gibi çok çeşitli farklı yapısal malzemelerin mekanik özelliklerini (örneğin, süneklik ve/veya tokluk) belirgin şekilde düşüren ciddi bir konudur. Bu tez çalışmasının amacı, FNSS Savunma Sanayi Sistemleri tarafından kullanılan MIL-DTL-12560 Class-4a ve MIL-DTL-46100 askeri şartnamelerini sağlayan zırh çeliklerinin hidrojen gevrekleşme davranışlarını deneysel yöntemlerle araştırmak ve hidrojen geri difüzyon operasyonu için sıcaklık ve zaman parametrelerini optimize etmektir. Bu kapsamda, hidrojene maruz kaldığında mekanik özelliklerin olumsuz şekilde etkilendiğini tespit etmek için, iki farklı zırh çeliğinin hidrojen yüklü ve hidrojen yüklü olmayan numuneleri ile tek eksenli çekme, basma, yüksek gerinim hızı, sertlik, darbe ve balistik testler de dahil olmak üzere çeşitli mekanik testler gerçekleştirildi. Deneysel çalışmalarda kullanılmak üzere gerekli olan hidrojen yükleme işlemi, bir elektrokimyasal hidrojen sistemi kullanılarak gerçekleştirilmiştir. Son olarak, hidrojenli ve hidrojensiz numunelerin kırılma yüzeylerinde mikroyapısal analizler gerçekleştirilmiştir. Mikroyapının mekanik özelliklere etkisi ayrıca araştırılmıştır.
Citation - WoS: 22
Citation - Scopus: 23
Strain Rate and Hydrogen Effects on Crack Growth From a Notch in a Fe-High Steel Containing 1.1 Wt% Solute Carbon
(Pergamon-Elsevier Science Ltd, 2020) Najam, Hina; Koyama, Motomichi; Bal, Burak; Akiyama, Eiji; Tsuzaki, Kaneaki
Effects of strain rate and hydrogen on crack propagation from a notch were investigated using a Fe-33Mn-1.1C steel by tension tests conducted at a cross head displacement speeds of 10(-2) and 10(-4) mm/s. Decreasing cross head displacement speed reduced the elongation by promoting intergranular crack initiation at the notch tip, whereas the crack propagation path was unaffected by the strain rate. Intergranular cracking in the studied steel was mainly caused by plasticity-driven mechanism of dynamic strain aging (DSA) and plasticity-driven damage along grain boundaries. With the introduction of hydrogen, decrease in yield strength due to cracking at the notch tip before yielding as well as reduction in elongation were observed. Coexistence of several hydrogen embrittlement mechanisms, such as hydrogen enhanced decohesion (HEDE) and hydrogen enhanced localized plasticity (HELP) were observed at and further away from the notch tip resulting in hydrogen assisted intergranular fracture and cracking which was the key reason behind the ductility reduction. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Citation - Scopus: 1
Data-Driven Discovery and DFT Modeling of Fe4H on the Atomistic Level
(Elsevier B.V., 2024) Zagorac, Dejan; Zagorac, Jelena; Djukic, Milos B.; Bal, Burak; Schön, Johann Christian
Since their discovery, iron and hydrogen have been two of the most interesting elements in scientific research, with a variety of known and postulated compounds and applications. Of special interest in materials engineering is the stability of such materials, where hydrogen embrittlement has gained particular importance in recent years. Here, we present the results for the Fe-H system. In the past, most of the work on iron hydrides has been focused on hydrogen-rich compounds since they have a variety of interesting properties at extreme conditions (e.g. superconductivity). However, we present the first atomistic study of an iron-rich Fe4H compound which has been predicted using a combination of data mining and quantum mechanical calculations. Novel structures have been discovered in the Fe4H chemical system for possible experimental synthesis at the atomistic level. © 2024 Elsevier B.V., All rights reserved.
Hydrogen Susceptibility of Al 5083 Under Ultra-High Strain Rate Ballistic Loading
(Walter de Gruyter Gmbh, 2024) Baltacioglu, Mehmet Furkan; Mozafari, Farzin; Aydin, Murat; Cetin, Baris; Oktan, Aynur Didem; Teoman, Atanur; Bal, Burak
The effect of hydrogen on the ballistic performance of aluminum (Al) 5083H131 was examined both experimentally and numerically in this study. Ballistics tests were conducted at a 30 degrees obliquity in accordance with the ballistic test standard MIL-DTL-46027 K. The strike velocities of projectiles were ranged from 240 m s-1 to 500 m s-1 level in the room temperature. Electrochemical hydrogen charging method was utilized to introduce hydrogen into material. Chemical composition of material was analyzed using energy dispersive X-ray (EDX) analysis. Instant camera pictures were captured using high-speed camera to compare H-uncharged and H-charged specimen ballistics tests. The volume loss in partially penetrated specimens were assessed using the 3D laser scanning method. Microstructural examinations were conducted utilizing scanning electron microscopy (SEM). It was observed that with the increased deformation rate, the dominance of the HEDE mechanism over HELP became evident. Furthermore, the experimental findings were corroborated through numerical methods employing finite element analysis (FEM) along with the Johnson-Cook plasticity model and failure criteria. Inverse optimization technique was employed to implement and fine-tune the Johnson-Cook parameters for H-charged conditions. Upon comparing the experimental and numerical outcomes, a high degree of consistency was observed, indicating the effective performance of the model.
Çok Ölçekli Malzeme Modellemesi Yoluyla Talaşlı İmalat Çıktılarının Daha Kapsamlı Ve Doğru Analizi
(TUBİTAK, 2020) Bal, Burak; LAYEGH KHAVIDAKI, SEYD EHSAN
İnconel 718 savunma sanayi, uzay-havacılık ve otomotiv için kullanılan ve ileride kullanım alanı_x000D_ daha da genişleyebilecek olan süper alaşımdır. Bu projede Inconel 718 süper alaşımının talaşlı_x000D_ imalat sonucunda yüzeyinde oluşan kalıntı gerilimler, sertlik değişimleri ve kesici takımda oluşan_x000D_ aşınmalar gözlenmiştir. Talaşlı imalat simülasyonları için kullanılan Deform 2D programına, klasik_x000D_ Johnson-Cook malzeme modeli yerine, kristal plastisite tabanlı çok ölçekli malzeme davranışı_x000D_ tanıtılarak daha kapsamlı ve deneysel veriye daha yakın analizler yapılmıştır. Bu konunun seçilme_x000D_ nedeni, gerçek deneysel sonuçlara daha yakın sonuçlar elde edilip beklenmedik üretim hataları_x000D_ ve denemeleri en aza indirebilecek bir yöntem geliştirmektir. Bugüne kadar gerçekleştirilen talaşlı_x000D_ imalat simülasyonlarında malzeme davranışı genellikle tek ölçekli gerinim pekleşmesi, gerinim_x000D_ hızı pekleşmesi ve sıcaklık yumuşamasını kapsayan Johnson-Cook malzeme modelleri ile_x000D_ gerçekleştirilmiştir ve bu modeller malzemelerin mikroyapısal girdilerini içermemektedir. Bu_x000D_ projede ise Johnson-Cook malzeme modeli ile ve karşılaştırmalı olarak çok ölçekli kristal plastisite_x000D_ tabanlı malzeme modeli ile 2D deform programında farklı kesme hızlarında ve farklı ilerleme_x000D_ hızlarında simülasyonlar gerçekleştirilmiştir. Bu projede ilk olarak, Inconel 718 malzemesinin_x000D_ talaşlı imalat deneylerini yapılarak sonuçları gözlenmiştir. Daha sonra Johnson-Cook malzeme_x000D_ modellemesiyle gerçekleştirilen simülasyon sonuçları gözlenmiştir. Son olarak da Inconel 718_x000D_ süper alaşımının kristal plastisite modelinin yapılması ve mikroyapı girdileri ile elde edilen kristal_x000D_ plastisite modeli ile çıkarılan çok ölçekli ve çok eksenli malzeme davranışının Deform 2D_x000D_ simülasyonlarına tanıtılarak simülasyonu gerçekleştirip, elde edilen sonuçlar gözlenmiştir._x000D_ Yapılan simülasyonlar ve deney sonucunda, iki farklı malzeme modelin deneysel sonuçlarla_x000D_ karşılaştırılması yapılmıştır. Mikroyapı girdileri ile elde edilen kristal plastisite modeli ile çıkarılan_x000D_ çok ölçekli ve çok eksenli malzeme davranışının, tek ölçekli malzeme davranışı ile_x000D_ karşılaştırıldığında deneysel sonuçlara daha yakın sonuçlar verdiği gözlemlenmiştir. Böylelikle_x000D_ çok ölçekli malzeme modellemesiyle gerçekleştirilen simülasyonların daha gerçekçi ve güvenilir_x000D_ sonuçlar gösterdiği kanıtlanmıştır.
Citation - WoS: 2
Citation - Scopus: 2
Numerical Investigation of the Role of Volumetric Transformation Strain on the Relaxation Stress and the Corresponding Hydrogen Interstitial Concentration in Niobium Matrix
(Hindawi Ltd, 2017) Bal, Burak
The effects of relaxation stress on the hydrogen concentration in Niobium-(Nb-) H media were investigated by iterative numerical modeling approach. To calculate the transformation strain, relaxation stress, and corresponding relaxed hydrogen concentration around an edge dislocation, a new third-order polynomial formulation was utilized in the model. With the aid of this polynomial, hydrogen induced relaxation stress never exceeds the dislocation stress, which indicates that the total stress field never turns to compressive state and diverges the results. The current model calculates the hydrogen concentration not only in the vicinity of an edge dislocation but also far away from the dislocation. Furthermore, the effect of relaxation stress on the interaction energy was also captured in the model. Overall, the current findings shed light on the complicated hydrogen embrittlement mechanisms of metallic materials by demonstrating that hydrogen induced relaxation has a significant effect on the hydrogen atom concentration and the interaction energy between the existing internal stress field and the solute hydrogen atom.
Citation - WoS: 3
Citation - Scopus: 3
Investigations of Strain Rate, Size, and Crack Length Effects on the Mechanical Response of Polycaprolactone Electrospun Membranes
(Sage Publications Ltd, 2021) Bayram, Ferdi C.; Kapci, Mehmet F.; Yuruk, Adile; Isoglu, Ismail A.; Bal, Burak
The effects of strain rate, size (height x width), and pre-existing crack length on the mechanical response of polycaprolactone electrospun membranes were investigated by tension tests conducted at room temperature. In particular, tensile tests were performed with three different strain rates for strain rate effect tests, seven different geometries for elucidating the size effect, and three different initial notch lengths for crack growth experiments. The electrospun membranes were produced by the electrospinning technique using a polycaprolactone solution prepared in 1, 1, 1, 3, 3, 3-hexafluoro-2-propanol as the solvent. Scanning electron microscopy was utilized to show the continuous fiber structure without bead formation. The average fiber diameter was calculated as 1.113 +/- 0.270 mu m by using scanning electron microscopy images of the membranes. The chemical structure of polycaprolactone was analyzed by Fourier transform infrared spectroscopy, and the toxicity and cell viability of the electrospun membranes were shown by CellTiter 96(R) Aqueous One Solution Cell Proliferation Assay (MTS test). It was observed that the ultimate tensile strength and Young's modulus decreased, and the elongation at failure value increased as the strain rate decreased from 10(-1) to 10(-3) s(-1). Besides, positive strain rate sensitivity was observed on the mechanical response of electrospun polycaprolactone membranes. Moreover, the dependency of mechanical response on the size geometry has been well studied, and the optimum height and width combinations were specified. Also, crack growth was studied in terms of both macroscopic and microstructural deformation mechanisms and it is observed that individual fiber deformations and interactions are highly effective on the mechanical behavior and also propagation of the crack. Consequently, in this study, the size and strain rate effects and crack growth on the mechanical response of electrospun polycaprolactone membranes have been investigated extensively, and the results presented herein constitute an essential guideline for the usage of polycaprolactone electrospun membranes at different loading scenarios.
Citation - WoS: 4
Citation - Scopus: 4
A Phenomenological Hydrogen Induced Edge Dislocation Mobility Law for Bcc Fe Obtained by Molecular Dynamics
(Pergamon-Elsevier Science Ltd, 2024) Baltacioglu, Mehmet Furkan; Kapci, Mehmet Fazil; Schoen, J. Christian; Marian, Jaime; Bal, Burak
Investigating the interaction between hydrogen and dislocations is essential for understanding the origin of hydrogen-related fractures, specifically hydrogen embrittlement (HE). This study investigates the effect of hydrogen on the mobility of 1/2<111>{110} and 1/2<111>{112} edge dislocations in body-centered cubic (BCC) iron (Fe). Specifically, molecular dynamics (MD) simulations are conducted at various stress levels and temperatures for hydrogen-free and hydrogen-containing lattices. The results show that hydrogen significantly reduces dislocation velocities due to the pinning effect. Based on the results of MD simulations, phenomenological mobility laws for both types of dislocations as a function of stress, temperature and hydrogen concentration are proposed. Current findings provide a comprehensive model for predicting dislocation behavior in hydrogencontaining BCC lattices, thus enhancing the understanding of HE. Additionally, the mobility laws can be utilized in dislocation dynamics simulations to investigate hydrogen-dislocation interactions on a larger scale, aiding in the design of HE-resilient materials for industrial applications.
Tuning Mechanical Performance of PCL Scaffolds: Influence of 3D Bioprinting Parameters, Polymer Concentration, and Solvent Selection
(IOP Publishing Ltd, 2025) Ceylan, Saniye Aylin; Baltacioglu, Mehmet Furkan; Bal, Burak; Bayram, Ferdi Caner; Isoglu, Ismail Alper
The mechanical performance of three-dimensional (3D) bioprinted scaffolds is susceptible to printing parameters and material formulation. In this study, poly (epsilon-caprolactone) (PCL) scaffolds were fabricated using four different polymer concentrations (10%, 25%, 50%, and 75% w/v) to investigate how these variations, along with process parameters, influence mechanical behavior. Maintaining the structural integrity of bioprinted constructs requires careful optimization of polymer concentration and precise control over parameters such as printing speed, pressure, and infill density. Tensile tests were conducted to evaluate the effects of these variables. Among the tested conditions, a 50% (w/v) concentration allowed for a broader operational window, enabling fabrication across a range of printing speeds and pressures. At a printing speed of 5 mm s-1, PCL-DCM exhibited a Young's modulus of 39.0 MPa, while PCL-CF samples printed at 10 mm s-1 achieved the highest modulus of 32.0 MPa. Notably, when the printing speed was kept constant, applying higher pressures led to an increase in Young's modulus, suggesting that pressure plays a key role in enhancing scaffold stiffness. When comparing the 50% and 75% (w/v) polymer concentrations, the 50% (w/v) formulation stood out by offering both higher elongation and greater stiffness, which makes it particularly suitable for load-bearing applications. These findings provide a quantitative framework for optimizing extrusion-based bioprinting of PCL scaffolds, with implications for customized biomedical implants and regenerative medicine.
Citation - WoS: 14
Citation - Scopus: 16
Lowering Strain Rate Simultaneously Enhances Carbon- and Hydrogen-Induced Mechanical Degradation in an Fe-33Mn Steel
(Springer, 2019) Tugluca, Ibrahim Burkay; Koyama, Motomichi; Shimomura, Yusaku; Bal, Burak; Canadinc, Demircan; Akiyama, Eiji; Tsuzaki, Kaneaki
We investigated the strain rate dependency of the hydrogen-induced mechanical degradation of Fe-33Mn-1.1C steel at 303K within the strain rate range of 10(-2) to 10(-5)s(-1). In the presence of hydrogen, lowering the strain rate monotonically decreased the work hardening rate, elongation, and tensile strength and increased the yield strength. Lowering the strain rate simultaneously enhanced the plasticity-related effects of hydrogen and carbon, leading to the observed degradation of the ductility.
Citation - WoS: 12
Citation - Scopus: 16
Effect of Hydrogen on Fracture Locus of Fe-16Mn Twip Steel
(Pergamon-Elsevier Science Ltd, 2020) Bal, Burak; Cetin, Baris; Bayram, Ferdi Caner; Billur, Eren
Effect of hydrogen on the mechanical response and fracture locus of commercial TWIP steel was investigated comprehensively by tensile testing TWIP steel samples at room temperature and quasi-static regime. 5 different sample geometries were utilized to ensure different specific stress states and a digital image correlation (DIC) system was used during tensile tests. Electrochemical charging method was utilized for hydrogen charging and microstructural characterizations were carried out by scanning electron microscope. Stress triaxiality factors were calculated throughout the plastic deformation via finite element analysis (FEA) based simulations and average values were calculated at the most critical node. A specific Python script was developed to determine the equivalent fracture strain. Based on the experimental and numerical results, the relation between the equivalent fracture strain and stress triaxiality was determined and the effect of hydrogen on the corresponding fracture locus was quantified. The deterioration in the mechanical response due to hydrogen was observed regardless of the sample geometry and hydrogen changed the fracture mode from ductile to brittle. Moreover, hydrogen affected the fracture locus of TWIP steel by lowering the equivalent failure strains at given stress triaxiality levels. In this study, a modified Johnson-Cook failure mode was proposed and effect of hydrogen on damage constants were quantified. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Citation - WoS: 8
Citation - Scopus: 11
A Study of Different Microstructural Effects on the Strain Hardening Behavior of Hadfield Steel
(Korean Soc Steel Construction-KSSC, 2018) Bal, Burak
The effects of the initial texture, velocity gradient, strain increment and type of interaction tensor on the strain hardening response of Hadfield steel were investigated. To observe their influences on mechanical response, crystal plasticity computations were carried out with the aid of the Visco-Plastic Self-Consistent (VPSC) algorithm. Specifically, uniaxial deformation response of Hadfield steel was modeled based on the experimental deformation response at a strain rate of 1x10(-1) s(-1) and corresponding Voce hardening parameters were calculated. The same Voce hardening parameters were utilized with different boundary conditions in the VPSC simulations to identify the roles of the aforementioned microstructural properties. The current results demonstrate the importance of these microstructural properties for reliable predictions of the strain hardening response of Hadfield steel and constitute an important guideline for the proper selection of them.
Alüminyum 7068 Malzemesinin Mekanik Davranışlarının Hassas Olarak İncelenmesi ve Hasar Modelinin Araştırılması
(Abdullah Gül Üniversitesi, 2018) Karaveli, Kadir Kaan; Karaveli, Kadir Kaan; Bal, Burak
Yüksek mukavemet, yüksek tokluk, düşük yoğunluk ve korozyon dirençliliğinin ümit vaat eden kombinasyonu, onlarca yıldır alüminyum (Al) alaşımlarını binalardan havacılık sektörüne çeşitli uygulamalarda tercih edilen malzeme haline getirmiştir. Özellikle son zamanlarda geliştirilen malzemelerden bir tanesi olan Al 7068 alaşımı, olağanüstü mekanik ve mekanik özelliklerinden dolayı savunma sanayinde ve otomobil sanayinde kullanılmaktadır. Bu yüksek lisans tezinde, Al 7068-T651 alaşımının mekanik tepkisi ve Johnson-Cook hasar modeli araştırılmıştır. Özellikle, maksimum, minimum ve ortalama sonuçları dikkate alarak farklı uygulama alanları için farklı Johnson-Cook hasar parametreleri belirlenmiştir. Bu hasar parametreleri doğru Sonlu Elemanlar Analizi simülasyonları için kullanılabilir. Hasar parametrelerinin belirlenmesinde, hem hadde yönünde hem de hadde yönüne dik olarak çentikli ve düzgün numuneler üzerinde çekme deneyleri yapılmıştır. Çentik yarıçapı, farklı gerilim üçeksenliliği değerlerini sağlamak için pürüzsüz, 0,4 mm, 0,8 mm ve 2 mm olarak seçildi ve bu gerilim üçeksenliliği değerlerinde mekanik malzemenin tepkisi gözlemlendi. Çekme testleri, doğru sonuçları elde etmek için yedi kez tekrarlandı. Kırık numunelerin son kesit alanları optik mikroskop ile hesaplandı. Gerilim üçeksenliliği faktörünün ve hadde yönünün Al 7068-T651 alaşımının mekanik özellikleri üzerindeki etkileri başarılı bir şekilde araştırılmıştır. Tüm hasar parametreleri Levenberg-Marquardt optimizasyon yöntemi ile hesaplandı. Sonuç olarak, minimum, ortalama ve maksimum eşdeğer gerinim değerlerine dayanan üç farklı Johnson-Cook hasar parametresi hesaplanmıştır. Bu Johnson-Cook hasar parametreleri, bir hesaplama tekniği olan ve bu çeşitli mühendislik problemlerinin yaklaşık çözümünü elde etmek için kullanılan sonlu elemanlar analizinde farklı uygulamaların doğru hasar simülasyonları için kullanılabilir.
Citation - WoS: 10
Citation - Scopus: 12
On the Detailed Mechanical Response Investigation of PHBV/PCL and PHBV/PLGA Electrospun Mats
(IOP Publishing Ltd, 2019) Bal, Burak; Tugluca, Ibrahim Burkay; Koc, Nuray; Isoglu, Ismail Alper
In this study, electrospun mats of pristine poly(epsilon-caprolactone) (PCL), Poly(D, L-lactide-co-glycolide) (PLGA), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), as well as PHBV/PCL blends and PHBV/PLGA blends in different ratios (80:20, 75:25, 50:50, 25:75, 20:80, 10:90, 5:95%, w/w) and Centella Asiatica (CA) loaded (1, 5, 10%, w/v) PHBV/PCL and PHBV/PLGA polyester blends were prepared. Electrospun mats were characterized by scanning electron microscopy (SEM) in order to show uniform and bead and defect-free fiber structure with average diameter. The blend ratio and strain rate dependencies of mechanical behavior of these electrospun membranes were investigated under tensile loading. The tensile tests were conducted at an initial strain rates of 10(-1) s(-1), 10(-2) s(-1), 10(-3) s(-1) and 10(-4) s(-1) at room temperature and the best and worst combinations of PHBV/PLGA, PHBV/PCL blend ratios for both stress and ductility required applications were specified for each strain rate. The effects of blend ratios on the tensile strength and Young's modulus were also investigated. Moreover, the effects of Centella Asiatica on the electrospun membranes' mechanical behavior were demonstrated at different strain rates. Consequently, this study constitutes an important guideline for the selection and usage of the aforementioned electrospun membranes as a wound dressing material in terms of mechanical response at different loading scenarios.
Yapay Zeka Destekli Shot Peening Prosesinin Optimizasyonu ve İkincil Proseslerin SLM ile Üretilen AlSi10Mg Alaşımının Hidrojen Kırılganlık Direnci ve Mekanik Performansı Üzerindeki Etkilerinin İncelenmesi
(2025) Karaveli, Kadir Kaan; Bal, Burak
Bu tez, Seçici Lazer Ergitme (SLM) yöntemiyle üretilen AlSi10Mg alaşımlarında bilyalı dövme işlemlerinin optimizasyonunu ve hidrojen gevrekliğinin azaltılmasını araştırmaktadır. Birinci bölümde, süreç optimizasyon yöntemleri (ör. Taguchi, Box-Behnken), metal katkı üretimdeki (AM) sorunlar (artık gerilme, gözeneklilik) ve hidrojen gevrekliğinin mekanizmaları ile test yöntemleri ele alınmıştır. İkinci ve üçüncü bölümler, Almen testleriyle doğrulanan yapay zeka tabanlı yaklaşımlarla bilyalı dövme yoğunluğunun optimizasyonunu ve Bell 412EP ile Piper PA-32R gibi gerçek havacılık arızalarını inceleyerek hidrojen gevrekliğinin bileşenlerdeki etkilerini analiz etmektedir. Dördüncü ve beşinci bölümler, SLM ile üretilen AlSi10Mg alaşımlarının mekanik performansına, gerinim hızı ve işlem sonrası uygulamaların (bilyalı dövme, ısıl işlem) etkilerini değerlendirmiş ve yorulma direncinde önemli iyileşmeler göstermiştir. Ayrıca hidrojen gevrekliğini önlemek için ileri düzey stratejiler önerilmiştir. Tez, artırılmış malzeme güvenilirliği ve sürdürülebilirliğin toplumsal faydalarını vurgulamakta ve yapay zeka destekli yöntemler ile üretimde gerçek zamanlı izleme sistemleri üzerine gelecekteki araştırmaları önermektedir.
Citation - WoS: 10
Citation - Scopus: 10
Edge Dislocation Depinning From Hydrogen Atmosphere in Α-Iron
(Pergamon-Elsevier Science Ltd, 2024) Kapci, Mehmet Fazil; Yu, Ping; Marian, Jaime; Liu, Guisen; Shen, Yao; Li, Yang; Bal, Burak
Understanding the dislocation motion in hydrogen atmosphere is essential for revealing the hydrogen-related degradation in metallic materials. Atomic simulations were adopted to investigate the interaction between dislocations and hydrogen atoms, where the realistic hydrogen distribution in the vicinity of the dislocation core was emulated from the Grand Canonical Monte Carlo computations. The depinning of edge dislocations in alpha-Fe at different temperatures and hydrogen concentrations was then studied using Molecular Dynamics simulations. The results revealed that an increase in bulk hydrogen concentration increases the flow stress due to the pinning effect of solute hydrogen. The depinning stress was found to decrease due to the thermal activation of the edge dislocation at higher temperatures. In addition, prediction of the obtained results was performed by an elastic model that can correlate the bulk hydrogen concentration to depinning stress.
Citation - WoS: 31
Citation - Scopus: 31
A Detailed Investigation of the Effect of Hydrogen on the Mechanical Response and Microstructure of Al 7075 Alloy Under Medium Strain Rate Impact Loading
(Pergamon-Elsevier Science Ltd, 2020) Bal, Burak; Okdem, Bilge; Bayram, Ferdi Caner; Aydin, Murat
Effects of hydrogen and temperature on impact response and corresponding microstructure of aluminum (Al) 7075 alloy were investigated under medium strain rate impact loading. The specimens were subjected to impact energy of 12 J and 25 J, corresponding to impact velocities of 2.13 m/s and 3.08 m/s, respectively. These energy levels were decided after a couple of impact tests with different impact energy values, such as 6 J, 10 J, 12 J, 25 J. The experiments were conducted at five different temperatures. Electrochemical charging method was used for hydrogen charging. Microstructural observations of hydrogen uncharged and hydrogen charged specimens were carried out by scanning electron microscope. Hydrogen changed the crack propagation behavior of Al 7075 alloy depending on the temperature. Coexistence of several hydrogen embrittlement mechanisms, such as hydrogen enhanced decohesion (HEDE) and hydrogen enhanced localized plasticity (HELP) were observed under impact loading. The impact response of Al 7075 was significantly deteriorated by the hydrogen charging and changing temperature affected the absorbed energy of hydrogen-charged specimens. In addition, molecular dynamics simulations were conducted to uncover the atomistic origin of hydrogen embrittlement mechanisms under impact loading. In particular, hydrogen decreased the cohesive energy and enhanced the average dislocation mobility. Therefore, the experimental results presented herein constitute an efficient guideline for the usage of Al alloys that are subject to impact loading in service in a wide range of temperatures. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Numerical Study of Magnesium-Based Metal Hydride Reactor Incorporating Multi-Phase Heat Exchanger for Thermal Energy Storage System
(Scanditale AB, 2020) Yao, Jing; Zhu, Pengfei; Ren, Jianwei; Kapci, Mehmet Fazil; Bal, Burak; Kurko, Sandra V.; Zhang, Z. X.
Metal hydride based thermal energy storage system is regarded as a promising method due to its good reversibility, low cost, and no by-product. Multi-phase heat exchange has much higher heat transfer coefficient than single-phase fluid heat exchange, thus facilitating the steam generation. In this study, a two-dimensional model of the metal hydride reactor using multi-phase heat exchange is proposed to estimate the performance and its feasibility of application in the concentrated solar power system. The results show that the velocity of the heat transfer fluid should match well with the thermal conductivity of the metal hydride bed to maintain the heat flux at a relatively constant value. The match of thermal conductivity of 3 or 5 W/(m·K) and fluid velocity of 0.0050 m/s results in the heat flux up to about 19 kW/m2, which is increased by 3 orders of magnitude than single-phase heat exchange. This study helps to facilitate the widespread application of metal hydride based thermal energy storage system in the concentrated solar power system. © 2024 Elsevier B.V., All rights reserved.